Technology to obtain protein materials by recombinant expression of various gene products simultaneously and in parallel using Escherichia coli is very important in the scientific field of structural proteomics/functional proteomics which is generally called post-genomics.
In order to obtain a protein sample from a gene of interest, conventionally, the gene of interest was amplified by PCR; the resultant PCR product was ligated into a sub-cloning vector, with which a host was transformed; the transformed host was allowed to form single colonies; plasmid was purified from the host derived from each colony; the nucleotide sequence of the plasmid was determined to thereby select those clones in which the gene of interest was inserted. Subsequently, a DNA fragment containing the gene of interest was cleaved out from the selected clone using restriction enzymes; the cleaved DNA fragment was purified and then integrated into a fusion protein expression vector; a host was transformed with the vector; the transformed host was allowed to form single colonies; plasmid was purified from the host derived from each colony; a host bacteria for protein expression was transformed with the purified plasmid to thereby express the protein encoded by the gene of interest. The above-described operations are time-consuming; they require nine days at the quickest. Besides, the step of cleaving DNA fragments containing the gene of interest from the sub-cloning vector using restriction enzymes and the step of purifying the resultant DNA fragments require skill.